German Patent Application No. DE 102 21 498 A1 describes a method for manufacturing a capacitor having an inert porous mold to which a first electrically conductive layer, a barium titanate layer, and then an electrically conductive layer are applied.
However, since the substrate, designed as a mold, of such a capacitive storage element is porous, the design of the titanate layer as a layer which is designed as a through-layer having a thickness which ensures adequate dielectric strength is not easy to achieve since the titanate is deposited preferably in the recesses in the porous substrate, while the protruding parts of the porous substrate remain uncovered by titanate or are only inadequately covered.
The minimal local thickness of the titanate layer, i.e., the thickness of this layer in its thinnest place, generally determines the dielectric strength of the capacitive storage element. Therefore, a corresponding local minimum thickness of the titanate layer is necessary for the particular use of the storage element. At the same time, however, the layered nature of the titanate layer should be ensured, i.e., the ratio of the layer thicknesses in the place having the greatest layer thickness to that having the smallest layer thickness should not be excessively high.
One preferred application of electrical storage elements such as electrochemical storage elements or capacitive storage elements is their use as storage elements of an electrical energy storage unit for supplying energy to an electric drive or a hybrid drive of a motor vehicle. An electrical energy storage unit is required for operating the electric drive train of an electric drive or a hybrid drive of a motor vehicle; the electrical energy storage unit has storage elements (storage cells) and, on the one hand, has a limited weight, so that it may be carried in the vehicle, and, on the other hand, is still able to store a sufficient amount of energy to ensure the usual range of a motor vehicle, such as of a passenger vehicle. Electrochemical energy storage units designed as rechargeable batteries or accumulators having lithium ion cells are considered to be the most effective energy storage units today. Today, the corresponding lithium ion batteries have an energy density of less than 0.2 kWh/kg. Additional selection criteria for selecting the type of energy storage unit include, in addition to the energy density, in particular the service life, the required top performance and the energy efficiency. In addition, costs and environmental safety also play a crucial role in the selection of the type of energy storage unit.
Since the energy storage units for supplying energy to an electric drive or a hybrid drive of a motor vehicle are charged with a relatively high charging voltage of approximately 400 V to 600 V, the individual storage elements (storage cells) must have a corresponding dielectric strength (breakdown rating), depending on their wiring within the energy storage unit. With the aforementioned capacitive storage elements, this dielectric strength depends to a significant extent on the minimum local thickness of the titanate layer.